Associated resonant circuits



y 1929. J. 5. STONE 1.720.770

ASSOCIATED RESONANT CIRCUITS 7 Filed July ll, 1924 2 Sheets-Sheet 6, AMPL/F/EE 0 IN VEN TOR fimJza/rw diam BY A TTORNE Y y 16, 1929- J. s. STONE ASSOCIATED RESONANT CIRCUITS 1924 2 Sheets-Sheet Filed July ll IN VEN TOR Jafin/ 0120 Jtoiw A TTORNE Y li qflancy Funcdam w g x Patented July 16, 1929.

UNITED/STATES PATENT orrlca.

JOHN STONE STONE, OF SAN DIEGO, CALIFORNIA, ASSIGNOB TO AMERICAN TEEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF'NEW YORK.

ASSOCIATED RESONANT CIRCUITS. I

Application filed July 11,

An object of my invention is to provide new and improved apparatus and method for the reception of currents of a determinate frequency range or band, with only a determinate amount of distortion within that range and the practical exclusion of currents lying outside that range. Another object of my invention is to combine resonant circuits and amplifiers so as to secure sharp selectivity 1 for a desired frequency band of substantial width with but a small determinate amount of distortion within that hand. These and various other objects of my invention will be made apparent in the following specification and claims, taken with the accompanying drawings, in which I have illustrated a limited number of specific embodiments of the invention. It will be understood that the invention is defined in the appended claims and that the following description relates more particularly to these examples of the invention which are shown by way of illustration.

Referring to the drawings, Figure 1 is a diagram of a resonant circuit; Figs. 2, 3, 4, 5, r 6 and 7 are respective diagrams of resonant circuits designed and associated in accordance with the principles of my invention; Fig. 8 is a curve diagram illustrating the results obtained with eight associated circuits as compared with a single circuit; and Figs. 9 to 12 are further diagrams of resonant circuits designed and associated according to a, modified embodiment of my invention.

Referring to Fig. 1, this represents a simple circuit with capacity (3,. inductance L and resistance R,. Let a simple harmonic electromotive force of amplitude E, and frequency f be applied to this circuit. Then the amplitude of the resulting current is well known to be given by the equation where *w=21rf. The resonance frequency f is given by 1924. Serial No. 725,488.

From the that foregoing it can readily be shown x $4 ff.

Define selectance S by the equation fi m, h a m (3 Then Equation (3) can be expressed As will be seen from the discussion that follows, there is an advantage in using the frequency function (1 instead of the frequency f as the independent variable in connection with problems involving resonant circuits. The frequency function a is obviously zero for resonance, that is for /=f and it is -00 for f=0, and +00 for f=oo.' The resonance curve with respect to a is symmetrical about its maximum ordinate, whereas the resonance curve with respect to f is unsymmetrical about its maximum ordinate.

Let the two frequencies f, and f, be assigned, for which the circuit of Fi 1 is to be designed to give the same amp itude of current I for the same amplitude of impressed electromotive force E,. It follows at once that a =a or a =iu whence it is readily deduced that f0 N L f2 (4.)

to f as a frequency band, it will be seen that the resonance frequency is a mean proporand at resonance I and tional between the terminal frequencies, and it will here be termed the medial frequency of the band. The function will here be termed the frequency function of this band.

Let it be required that for a. constant amplitude of impressed electromotive force E the amplitude of the current I at the termi nal frequencies f, and 1, shall be of the amplitude at resonance. Accordingly, it follows from Equation (4) that =i R1 m m 1 From this it follows that m 1 0M2 we 12 1 17 2) 1 ''f2) 2 S: \f iz' Substitutin from Equations (2) and (3) in Equation and solving, the result is obtained that /m 1 R I 9 L1 "(f1 f2) l Substituting this value of L in Equation 2 and also substituting from Equation (4),

giving the ratio of the current at resonance frequency f, to the currents at the terminal frequencies f, or f We now proceed to inquire What are the frequencies (greater than 7, and f (less than f at which, for a given amplitude of impressed electromotive force E the amplitude of the currents will be equal and each will be 1 times the amplitude of the current at resonance for the same electromotive force E The condition is expressed thus:

Solving this equation, the result is readily obtained that T: a i 1 (11) but from Equation (5) 1: m 17 -10 a f and a J d From these equations and from Equation (11) the solutions for f and f; are obtained as follows:

-1 4S2 f'FJpTsh/ a -1*) As a numerical example to illustrate the foregolng, couslder a band of frequencies from f =102,000 to f =98,000. lVe may consider that we are dealing with a carrier current whose frequency is 100,000 and thatit is modulated by current of frequency from zero to 2,000. The resulting frequencies will lie within the band range that has been assigned.

, The frequency f the medial frequency of the frequencies f and f shall be of the amplitude at the resonance frequency f Then m= and from Equations (8), (9) and (10), S= 12.106, L =1.927 X10" R and \Vith the foregoing illustration it will be seen that we have now provided an analysis which gives the conditions for the reception by a simple resonant circuit of a band of frequencies with a determinate amount of distortion within the band. We have also provided (in connection with the values f and 7'' for determining the degree of exclusion of frequencies differing by a determinate amount from the medial frequency of the band.

Let p=100. This means that f and f of Equations (12) will give us the frequencies for which, with the same impressed electromotive force, the amplitude of the current will be but 1% of that at the resonance frequency f Substituting in Equations (12) and evaluating, the results are obtained that f =838,000 and f =11,900.

With the single circuit of Fig. 1, the requirement for distortion to be restricted with in the ratio results in small selectivity.

The exam le that has just been worked out correspon s to a simple telephone receiving circuit when the carrier frequency is 100,000, when both side bands are transmitted and .are two resonant circuits 1 .and 2, each having the same selectance S and each tuned to the frequency f It should be noted that the condition of equal selectance S for the two circuits does not imply that R,, L and C are respectively equal to R,, L and C A is a relay or amplifier of such character and so connected between the two circuits that the amplitude of the impressed electromotive force E. in circuit 2 is proportional only to the amplitude of the current I, in circuit 1.

That is, E =K 1,, where K is a constant independent of frequency. Accordingly, when a simple harmonic electromotive force of amplitude E and frequency f is impressed on the first circuit, theamplitude of the curwhere R, is the resistance of circuit 4.

' In general, let there be 71. circuits each tuned to the common frequency f, and each having the selectance S. Let each of these circuits except the first be so coupled to its antecedent circuit in order through a relay that the amplitude of the electromotive force impressed rent in the second circuit will be (by Equat i where R is the resistance of the second circuit.

The idea of Fig. 3 will readily be apparent. Circuits 1 and 2 and their connection are the same as for Fig. 2. The third circuit 3 has the same selectance S and is tuned to the same frequency f and the relay A is of such character and so connected between the circuits 2 and 3 that the amplitude .of the electromotive force E in circuit 3 is proportional only to theamplitude of the current flowing in circuit 2, that is 3 K212 and K 1 1 K K E 1 4) w R (1 (1 8 1 2 a where R, is the resistance of circuit 3. Similarly for Fig. 4,

upon it shall be proportional only to the amplitude of the current flowing in its antecedent circuit. Then the amplitude of the current in the nth or last circuit resulting from an impressed simple harmonic electromotive force of amplitude E and frequency f in the first circuit will .be

/=R1R2R3 where R, is the resistance of the jth circuit. The number n may be the number of any intermediate circuit or it may be the number of the last circuit of the sequence. Whatever value is given to n within the total number of circuits in the sequence, the foregoing Equation (16) gives the current in the correspondingly numbered circuit of the sequence.

Let the band of frequencies to be received extend from f, to f as in the casealready considered for the single circuit of Fig. 1. For the same amplitude of impressed electromotive force in circuit 1, let the amplitude of the current in circuit at be the same for the extreme frequencies f, and f The'medial frequency of the band, the resonance frequency, will be f6 V flfz Represent the expression K K2K3 K mpE R R R R,

in Equation (16) by F. When the frequency is f,,, a=0 and Equation (16) becomes I}, (f,,) =F. As before, let the current at f, and

f, be of the current at f Then From Equations (3), (16'), (2) and (4), 105

the result is obtained that The resistances R of the circuits in sequence are the resistances which reside in the inductances L as indicated in the drawings, but the inductances L and the capacities C have progressively different values as given by Equations (17) and (18) That is, an 1nspect1on of these equations shows that in the successive circuits, the inductance L is given by giv ng successive integer values to n in Equation (17). Similarly, the capacity C in each Cl1- cuit is found by giving a proper value the number n in Equation (18) Thus it will be seen that the inductances and capacities of the successive circuits are progressively different from circuit to circuit.

By a procedure arallel to that for Equations (12) it is d8l0d that To illustrate the principles that have been worked out in the foregoing discussion, consider the construction of a system of eight connected circuits each tuned to the common frequency f,,, each having the common selectance S, and between each pair of successive members a relay so designed and so connected that the amplitude of the electromotive force impressed upon the output circuit shall be proportional only to the amplitude of the current in the input circuit. Let this system of associated resonant circuits be required to pass a band of frequencies between f,=102,000 and f =98,000, with a limit of 10% distortion as for the case of the single circuit of Fig. 1 already considered. As in that case, the carrier frequency is f =100,000, the medial or resonance frequency is f,,=99,980 and the frequency function for the band is a, =O,O40,008. However, in this case the ultimate value of S is no longer the same as for Fig. 1 but is now given by substituting in Equation (18*) with result as follows:

Also from Equations (17 and (18) i L =6.5O 10 R A comparison of the values of f, and f that were obtained for the single circuit of Fig. 1 with the values for the eight associated circuits now considered is given below, the band width being the same in both cases.

and

Eight circuit filter. Band. Single circuit.

100,000 f',= 85,000 f, 98,000 f',= 11,900

This comparison is also exhibited in Fig. 8.

-In all the illustrations that have been considered heretofore, we have assumed a carrier frequency of 100,000. It will be instructive now to assume a carrier frequency of 1,000,000 with the same band Width as before, that is, the band extends from f,=1,002,000 to f =998,000. As before, a distortion of 10% only is permitted and a system of eight associated resonant circuits is compared with a single circuit. The results are given in the following table:

Eight circuit filter. Band. Single circuit.

f,=1,026,000, f,1,002,000 f,=1,494,000 f.1,000,000 f 974,500 f, 998,000 f',= 009,000

Comparing the two tables, it will be seen that the ability of the system of associated reso-' nant circuits to exclude frequencies lying outside the band is greater, the higher the carrier frequency; for this reason a larger number of elements would need to be employed for of such elements.

low carrier frequencies than for high carrier frequencies.

The formula for the number of simple circuits required to reduce the amplitude of the value for any particular frequency is deduced from Equation (16) this gives current to the fraction of its resonance whence In practice the next larger whole number than n of the foregoing equation will be taken.

It will be seen that for a preassigned band of frequencies and a preassigned degree of permissible distortion, we have (a) tuned all the component circuits to the same frequency, namely the medial frequency of the band, (6) made the selectance the same in all the component circuits, namely S, but while S is a function of capacity (C), inductance (L) and resistance (R), these values are not the same in all the component circuits, and (0) we have so associated each component .circuit with its antecedent circuit that the quencies greater than i and less than f, b v

(d) employing a determinate number (n It now remains to show how the required coupling between the successive circuits can be effected.

One method is illustrated in Fig. 5 in which each resonant circuit is coupled with its antecedent circuit through a relay'whose input is shunted across a resistance in the antecedent circuit and whose output. is shunted across a resistance in the consequent circuit. Another method of coupling the circuits is illustrated'in Fig. 6. Each resonant circuit is coupled Withits antecedent circuit through a relay whose input is shunted across a portion of the reactance of the antecedent circuit and whose output is shunted across a pore tion of the reactance of the consequent circuit. The reactances shunted in this way are different from each other for the reason that otherwise the amplitude of the electromotive force impressed upon any given circuit of the combination would not be solely roportional to the amplitude flowing in t f antecedent circuit but would be a functioflffzpf-t-he frequency of the current in that circuit as Well.

Fig. 7 shows still another way et -cou lin the circuits through the relays. In this case the amplitude of the electromotive force impressed on any given resonant circuit is not strictly proportional to the amplitude of the current in the antecedent circuit but the departure is compensated by alternating the character of the reactances which are shunted so that the amplitude of the impressed electromotive force in the last resonant circuit will be proportional to the amplitude of the current in the first circuit.

I will now disclose another embodiment of my invention, and for this purpose I will make reference to Figs. 9,10, 11 and 12.

Let the resistance, inductance, capacit and selectance of circuit 1 be R,, L,, C, and respectively, and let the corresponding constants of circuit 2 be R L C and S respectively. Let circuits 1 and 2 be resonant to frequencies f and f respectively. On circuit 1 let there be impressed a simple harmonic E. M. F. of amplitude E and froquency f, while on circuit 2, asimple harmonic E. M. F. of amplitude E and frequency f is impressed.

The amplitudes of the resulting currents in these two circuits will be respectively, where (1 and :1 are the frequency functions of circuits 1 and 2 respectively, these functions being defined as and rea

B nI a Then clearly from (24) and we have and v '40 1 1 (f1+fz) fin (fcl jl) j01 Un+fz fo1 (f'a1 f:)f01 h J1+adfl2s32 m 5 and a 91166 2 (f:+fz) fo2 (fe2'f1) fd2 2 (38) h U02 f 1)) 02 :2 f 1)) 02 em 82 1 9) 10 f01 (1:1 fz) c1 ".fz) 4121 T7? d f02 J (fcz' fl) (J02 f 4122 17? 7 S32 Z S12 12 a s, 2 (1525: iifog ifm I I -Q 2} 4 Under these conditions we have, I

01 15 and L I: 1 I I (41) as? :1: .70; R1 J1 i (m- Dani: If f z f are the extreme frequencies of a n 20 radio telephone band, and f if are the ex- I E, treme frequencies of a second telephone band, 2 then f and f are the carrier frequencies of 2 1 'i' (m 1);-, w the bands and f and f are the medial frea quencies of these bands. From the foregoe 0f the 'Cl11 S Is now tuned to the 25 ing we see that when a circuit is tuned to the l l frequency of its radlo frequency telemedial frequency of a hand then the circuit is equally responsive to the extreme frequen- Phone band" and each 18 m as lespomlve cies of the band.-. to the extreme fre uenciesof its hand as it Let is bevrequired that, for equal ampliis toits resonance requency. 30 tudes E of impressed E. M, F., the ampli- If now we associate these two circuits totude of the current 1 in circuit 1, for'fregether throu h a translating device D as ilh H b 1 h f h lustrated in jg. 10, and this association be quencles s a 6 i o t e reso such that the amplitude E of the impressed E1 E M. F. in circuit-2 is equal to K I where 35 1131106 P E' Then K is a numerical constant, then, for an impressed simple harmonicE. M. F. of ampli- 1 l (36) tude E and frequency f in circuit 1, the cur- /1 +a JS rent in circuit 2 will I I I I 1 I 5 1 a a a I (43) l J1+(m-1) -J1+(m 1)', I I I I w I 02*! When the fre uencies ofvthe force im- In the case of complete resonance, i. eiwhen 5 ressed u n the rst circuit are f t f and .the frequency impressed upon-circuit 1 is f those-of t e force impressed upon the second and that on circuit 2 is f then (43) recircuit are f ft, (43) reduces to duces to l I,= Kim/(m me) (4,5)

The difference between these frequencies is The difference between these medial frefb =f ,.f I I vquencies 1s f y-f But by and (33) I v 2 v t I 3 a 401 Jra-rz- 41; =fa 1 e- 1 Y I I Y Y I v For f uencies to excluded 41 and For radio telephony f? and are always: (42) sg effect to I I negligible compared to unity, so that we I I 5 have in effect, I I v I,=. 1a, s (48) j03' j0l fef fc1 fb1 7) I BMW-la, I ,It follows that if D in Fig. 10 is a beat reand I ceiv'er in which the beat frequency is f con- I I -j ditions (44) and (45) can be effectively I a na 4 nance value For the coupled system of Fig. 10 we therefore have substantially when a 01, and the amplitude I, be th its resonance value 1 when a m then where I2=E l (51) i z P As a numerical example, let the band of 1 1 I frequencles received extend from f 102,000 (52) to f" =98,000. The carrier frequencyof the 6 t n v 1 and y received band is f,, 2 100,000,

1 1 i ar Z, (53) f,= which equals 2,000 and the /1+(m-1) 2 v whence medial frequency of the received band is T- 1 401 vhf-j? 99,980.

=J g (54) Let the beat frequency f =900,000, then d. I I fc2 jc1 f: 1,000,000, and

Ja 'gwei If The band of frequencies impressed upon cirfzu f01 (56) cuit 2 extends from f" =998,000 to f n 1 1,002,000.

a, =F =F 0.04001, a, 1,= =F 1 0004000.

f 01 foa L19 1.; Let EFF) or m 9 then Let p 100, then a-2 9.83 \/100, 1 10-9 ,1= :l: 10 T 0.04001= 11.193 2 S Y 6940,8 8.331, 9 1

100 1 10-9 an= :i: 10 0.004000=0.1193 a 8', 0004000), 6944, 8 83.33. I 9 I 1 v 4 =2 .83 99 980X0.040 1 :1: 1 2 9 X 0 N 890x 0.001601 i 176,000 0 than 1% for all frequencies greater than 50,740 176,000 or less than 56,740.

1 070 000 In the case of a single circuit receiving such j,,={ a band with a similar limitation of the distortion, the frequencies for which the circuit From the foregoing we see that the orginiwould show a receptivity of less than 1% zation of Fi 10 permits of the reception of uld' e f 9 and f a telephone %and extending from f 102,000 The advantageEgained by h use Of he 0 11- to f=98,000 with a discrimination no great r pled system of 1g. 10 with the conditions than 10% against any frequency of the band 1m osed above is thus seen to be very marked.

and that this system has a receptivity of less uppose we have another pair of circuits,

3 and 4 of Fig. 11 associated together by means of a heat 1'eceiverD,, ,1n such a manner that the amplitude of the force E impressed made resonant respectively to frequencies f and f where f f equals 77, 7", hem the heat trequency of D then we have. he-

on circuit 4 is K, I Where K is a numerical cause of the similarity of the system to that 10 constant and 1,, is the amplitude of the current of Fig.

in circuit 3. If circuits 3 and 4 moreover be r '5 2 01 I4=E4/ R4'\/1+04 =E4/ R4 2 (04in I 2 2 3= f ff 63) SF 1/ l/aes 67) 03 S4: 1 m l/a i tg 1 i 64 9@ I22 25 a4 ffM I 3 04 fox (69) f i t -'f0 3 11 J 4 i1} 70 0; mm 3a 65) 2 1 t 20 f, 1 4

i c i i 1 71 a 1) FZfM (66) f1: 2 f04 4 z[\/1+ agaflflz I4: K E 1 1 R R 2 2 3 /1 (m 1) /1 (m 1) (72) Let this pair of circuits, 3 and 4 of Fig. lation f f =f,, f being the heat frequency 11,be associated with the pair of circuits 1 and of 1),. then if E =K E where K, is a 2 of Fig. 10 by means of a heat receiver D as numerical constant, we shall have illustrated in Fig. 12, and let us have the re- 1 K K K E 1 1 1 1 4- R R R R ""2 -2 2 ''T 1 2 3 4 2 2 3L J5; I 2 1 2* /1 +(m 1) /1+(m D /I l (m 1) \/1+(m D m- In this system, when the frequencies of the quency f is such as to produce resouanceof the force impressed upon circuit 1 are f,-,: f,, we 1 have i system, then mrg Thus if there are 8 1 9 h 1o I4 K1[(2Z(3E1/(RlRgfisR t -rt) (74) circuits, 11-8, and 1f t en m 0 and when the frequency impressed upon cirand "79-1:

cuit 1 is f We have the condition of reso- O nance of the system and j F s +=1e 67 s =4088 50 4 1 2 3 1/( 1 2 x 4) I l 0-001601 1 =100 100 1 10 3.1622 In general, if there be n circuits associated g2 1:2? 1 8 in the manner indicated, We have for iin- 2 21 22 I pressed frequencies f i-f, a g=81.0l S9 5" I,,=K, .K,,-,E /(R .R,,m") (7s) a= 81.01 =9.001 and for the condition of resonance 5 41.500 [FRI ,,,=4.500 0.04001 99,9s0

If the responsiveness of the nth circuit, when the transmitted irequencies are jqfl,

is to be- ;th of that when the transl'nitted fre- A comparison of these values of f with abruptly, the connections of the intermediate those of f given in the foregoing text between Equations (60) and (61) shows the advantage. gained by the successive association of the circuits contemplated in this memorandum.

The organization may be described as a sequence of circuits, associatedthrough frequency changing translating devices, in which each circuit is resonant to the frequency impressed upon it, in which the amplitude of the E. M. F. impressed upon each circuit is proportional to the amplitude of the current in its antecedent circuit, in which the selectivities of the circuits are severally proportional to their frequencies and in which the selectivity of the first circuit is given by the expression The transmitted frequencies at which the responsiveness of the nth circuit will be th that which it exhibits when the transmitted frequency is such as to produce a resonant response throughout the system is of the amplitude of the current in the nth circuit, when the transmitted frequency is such as topl'oduce resonance throughout the system to the amplitude of the current in this circuit. when t e transmitted frequencies are fqitfgthat'is to say, when they are the extreme-frequencies of the telephone band transmitted. I

In the'following claims theterm beat regenerated current of a ceiver refers to a receiver that receives current of a certain frequenc 'and also a locally different frequency,

and modulates them together and ives an output current which is the sum or difi'erence (or both sum and difference) of the two input frequencies.

-I claim: g

- 1. A plurality of resonant circuits and a plurality of translating devices alternating with them in succession, each intermediate translating device having its input connected with the antecedent resonant c rcuit and its output connected with the consequent resonant circuit, said resonant circuits having their inductances and capacities progressively difierent' from circuit'to circuit and proportioned so that in the output of the last of the series there shall be only 'a small determinate variation of current intensity over a determinate frequenc ran e and so that beyond said range said intensity shall diminish translating devices as aforesaid being such that the output electromotive force from each such device is proportional to the current in the corresponding antecedent circuit.

2. A plurality of resonant circuits and a plurality of translating devices alternating with them in succession, each intermediate translating device having its input connected with the antecedent resonant circuit and its output connected with the consequent reso- I nant circuit, said resonant circuits having their inductances and capacities progressively different from circuit to circuit and proportioned so that in the out ut of the last of the series there shall be on y a small determinate variation of current intensity over a determinate frequency range and so that beyond said range said intensity shall diminish abruptly, each said translating device constituting means to apply an electromotive force in the consequent circuit proportional to the current intensity in the antecedent circuit.

3. A plurality of resonant circuits having a plurality of translating devices arranged alternately in succession, each intermediate translating device having its input connected in shunt to a substantial part of the impedance of the antecedent resonant circuit and its output connected in series in the consequent resonant circuit, whereby the output electromotive force from such translatin device .will be proportional to the current 1n the circuit connected with the correspondin input to such device, said resonant circuits having their inductances and capacities progressively different from circuit to circuit and designed so that the ultimate output current of the system varies only a small permissible amount over a considerable desired frequency range and falls off abruptly outside that range. I

4. A plurality of resonant circuits and a plurality of translating devices alternatingand its out ut connected with the consequent resonant circuit, said resonant circuits. having respective selectance values proportional to frequency and the elements of the combination being of progressively different values from circuit to circuit andso pro ortioned and designed that there shall be on y a small determinate variation of current intensity over a determinate frequency range and so that-beyond saidv range said intensity shall diminish abruptlyr 5. In combination, a plurality'of resonant circuits havin a plurallty'o'f translating devices arrangeialte rnately in succession, said resonant circuits having s'electances proportional to frequency but having their inductances and capacities progressively different from circuit to circuit, each intermediate translating device having its input connected with the antecedent resonant circuit and its output connected with the consequent resonant circuit and comprising means to give an voutput electromotive force proportional to the input current so that; the ultimate output current of the system varies only a small per missible amount over a considerable desired frequency range and falls off abruptly out-' sidethat range.

6. A plurality of resonant circuits and a plurality of beat receivers alternating with minate frequency range and so'that beyond said range said Intensity shall diminish abruptly.

A plurality of resonant circuits and a plurality of frequency changing translating devices alternating with them in succession, each intermediate translating device having its input connected with the antecedent resonant circuit and its output connected with the consequent resonant circult, said resonant circuits being tuned to difi'erent fre quencies appropriate to said translating devices and having their resistance and reactance components proportioned so that in the output of the last of the series there shall be only a small determinate variation of current intensity over a determinate frequency range and so that beyond said range said intensity shall diminish abru tly.

8. A plurality'o resonant circuits and a plurality of frequency changing translating devices alternatin with them in succession, each said circuit fieing resonant to the frequency impressed upon it from the respective antecedent translating device, the amplitude of the electromotive force impressed upon each circuit being proportional to the amplitude of the current in the respective antecedent circuit and the selectances of the circuits be in respectively proportional to their resonant requencies.

9. Aplurality of resonant circuits and a plurality of frequency changing translating devices alternating with them in succession, each intermediate'translating device having its input connected with the antecedent resonant circuit and its output connected with the-consequent resonant clrcuit, each said circuit being resonant to the frequency impressed upon it from the respective antecedent translating device and the selectances of the said circuits being respectively proportional to their resonantfrequencies.

- Intestimony whereof, I have signed my name to this specification this 3d day of July 1924:. v

' JOHN STONE STONE. 

